New PIONEER SiriusXM-ready car stereo: What does the STATUS number mean?

On the display of my newly-installed Pioneer car stereo, when I am listening to SiriusXM, there is a number that displays on the second line of the display. All I can gather from the User Manual is that this is the STATUS. But of WHAT? The number changes occasionally, but not in any meaningful way, so it isn't a counter of any kind, neither does it correspond to anything obvious like what channel it is on, or what song is playing. For instance, today, on Siriusly Sinatra, the number was -0002. Then we changed to 50's on 50, and the number was -0212 at first, but later changed to -0213.

Can someone please explain exactly WHAT these numbers mean? Many thanks in advance :D